A disposable optrode using immobilized tyrosinase films.

A disposable fiber-optic sensor based on the immobilized tyrosinase enzyme in a composite biopolymer and its application for the detection of 3,4-dihydroxyphenyalanine (L-dopa) and its analog are described. The enzymatic oxidation product of L-dopa was stabilized through formation of an adduct with 3-methyl-2-benzothiazoline hydrazone resulting in enhanced accuracy and sensitivity of the measurements. The response was found to be linear and concentration dependent in the range of 5 x 10(-5) to 4 x 10(-4) M (r(2) = 0.9307) for the substrate l-dopa over the pH range 5.8 to 7.2 with response times of 8 min. The immobilized enzyme films are stable for 4 months when stored under moisture-free conditions at 4 degrees C.